The prior art is replete with various types of devices for controllably varying the phase and amplitude of an electrical signal applied thereto. These variable phase shifter/amplitude weighting devices are utilized in a wide variety of applications, e.g., in beam forming and steering networks (BFSN's) for phased array antennas such as are employed in radar and satellite communications systems.
Phased array antennas are generally comprised of a multiplicity of individual radiating or antenna elements which are geometrically configured in accordance with the desired coverage and beam characteristics of the particular phased array antenna under consideration. For example, the antenna elements may be arranged in a one-dimensional linear array, a PG,3 two-dimensional planar array, or a three-dimensional circular array. The array of individual antenna elements cooperate in a well-known manner, e.g., in a transmit mode of operation, to produce a focussed beam of electromagnetic radiation (e.g., a microwave RF-signal) having a desired far field pattern pointed in a desired direction, to thereby provide a desired beam coverage area. More particularly, each of the antenna elements is fed with RF power at controlled relative phases and amplitudes to form the focussed beam having the desired shape and pointing direction. The required phase and power/amplitude distributions have been implemented by various forms and combinations of beam forming and steering networks incorporating variable phase shifter and power dividing (amplitude weighting) devices which controllably couple a common source of RF power to the individual antenna elements of the phased array antenna. The resultant beam produced by this excitation of the antenna elements may be electronically steered to any desired beam scan angle within a 360.degree. azimuth coverage area, e.g., under the control of a phase selecting or switching matrix, such as a Butler matrix. The precision, accuracy, and reliability of these beam forming and steering networks are largely dependent upon these characteristics of the variable phase shifter and amplitude weighting components employed therein. These characteristics of the present state-of-the-art phase shifter and amplitude weighting devices are unduly constrained.
More particularly, the current state-of-the-art phase shifter and power dividing devices are implemented as I/Q weighting circuitry, wherein an incoming RF-signal is split into I and Q components which are in phase quadrature with each other, with each signal component being independently phase shifted by either 0.degree. or 180.degree. and thence, independently attenuated (i.e., amplitude weighted). Full four-quadrant variable phase and amplitude control over the incoming RF-signal is achieved by adjusting the setting of the attenuators and switching the phases (between 0.degree. and 180.degree. ) of the signal components I and Q.
One major shortcoming of these current state-of-the-art variable phase shifter and power dividing devices is that they are limited in resolution, at best, to approximately 2.degree. phase shift increments, depending on the attenuation limits. Another major shortcoming of these state-of-the-art variable phase shifter and power dividing devices is that they are inherently inaccurate and unreliable. More particularly, these devices utilize analog components, such as attenuators, which exhibit drift, over time and temperature. The analog attenuators, in particular, exhibit variations and non-linearities in their intercept point and amplitude flatness at different attenuation settings over the operating frequency band. Further, these devices are somewhat bandwidth-limited in that they are inaccurate over broad bandwidths.
Based on the above and foregoing, it can be appreciated that there presently exists a need for a variable phase shifter and amplitude weighting device which overcomes, or at least minimizes, the above-delineated shortcomings associated with the presently available variable phase shifter and amplitude weighting devices.
The present invention fulfills this need, in a manner which will become apparent from the ensuing brief and detailed descriptions thereof.